The present invention relates to an electric household appliance and the control method for it, in particular a method for defrost control of an electric household refrigerator and refrigerators which use this method.
When an electric household refrigerator is in use, a coating of frost inevitably forms on the evaporator of the chilled storage compartment and the freezer compartment. It is therefore necessary to start the heating unit installed on the evaporator at regular intervals (this is generally a heating filament in proximity to the evaporator fins), to defrost the evaporator and to convey the melt water away by way of a drainage pipe. The refrigeration control of the refrigerator correspondingly also comprises a chill cycle to chill the storage compartment and a defrost cycle to defrost the evaporator.
A defrost method for electric household refrigerators is disclosed in the U.S. Pat. No. 6,694,755 B2. In the defrost cycle the evaporator is defrosted by starting the heating unit for a preset time period. Once the heating unit has been turned off, before the compressor is started to perform the normal refrigeration cycle, the refrigeration system is stopped for a preset time period, so that the defrost water that has melted on the evaporator can disappear completely from the evaporator and be conveyed away. This preset time period is referred to as drip time.
However this defrost method also has shortcomings. For example the evaporator fan is generally positioned in proximity to the evaporator. The high level of moisture around the evaporator means that during the course of the defrosting of the evaporator a thin layer of water droplets generally forms on the fan blades of the evaporator fan and on the inner surface of the evaporator chamber in proximity to the fan blades due to condensation. Once the heating operation of the heating unit stops, regardless of whether there is drip time or the compressor is started immediately to perform the refrigeration cycle, the temperature of the evaporator chamber drops rapidly. As a result the water droplets on the fan blades of the evaporator fan and on the inner surface of the evaporator chamber in proximity to the fan blades condense very quickly and form a coating of frost. This blocks the space for rotation of the fan blades between the fan blades of the evaporator fan and the inner surface of the evaporator chamber, preventing the evaporator fan starting normally.